Solve for $x$ and $y$ using substitution. ${5x+4y = -4}$ ${y = -2x-7}$
Solution: Since $y$ has already been solved for, substitute $-2x-7$ for $y$ in the first equation. ${5x + 4}{(-2x-7)}{= -4}$ Simplify and solve for $x$ $5x-8x - 28 = -4$ $-3x-28 = -4$ $-3x-28{+28} = -4{+28}$ $-3x = 24$ $\dfrac{-3x}{{-3}} = \dfrac{24}{{-3}}$ ${x = -8}$ Now that you know ${x = -8}$ , plug it back into $\thinspace {y = -2x-7}\thinspace$ to find $y$ ${y = -2}{(-8)}{ - 7}$ $y = 16 - 7$ $y = 9$ You can also plug ${x = -8}$ into $\thinspace {5x+4y = -4}\thinspace$ and get the same answer for $y$ : ${5}{(-8)}{ + 4y = -4}$ ${y = 9}$